If someone is offended that you ask them not to pet your dogs then that is their problem, not yours. I agree with cell that if people are calm and appropriate and ask, then sure it is a great opportunity for socialization. But you have to do what is best for your dogs and if you can tell that someone, especially kids, don't know how to meet a dog properly then that is dangerous for your dog and a liability to you. You are perfectly within your rights to say no, and just explain that you're working on some training with your dogs.
Chase (Friendly Resident Wigglebum) - Border Collie/Lab/Shepherd X
Kailey (Misunderstood Gentle Beauty) - GSD & foster failure #1
Rupert (Gold-Medal Winner of the 3 a.m. Kitty Destruction Olympics
Heidi - RIP my sweet baby girl